A variety of different types of therapeutic and/or diagnostic implantable medical devices, including implantable pacemakers, cardioverters, defibrillators, neural stimulators, and the like, have been shown in the prior art. Often, such implantable medical devices employ an hermetically-sealed electronic component, such as a pulse generator and/or a sensing circuit, in conjunction with one or more flexible, implantable, electrically conductive leads. For example, pacing and sensing leads are used in pacemaker systems to convey electrical stimulating pulses from an implanted pulse generator to the patient's heart, and to convey electrical cardiac signals from the heart to implanted sensing circuitry associated with the pulse generator.
In systems employing an implantable lead, lead infection resulting from the introduction of bacteria at the implant site at the time of implant is a rare but serious complication. In the prior art, it has been suggested to coat the lead with anti-microbial substances in order to reduce the risk of infection. However, the more common and much more serious--possibly life-threatening--complication is the possibility of infection at the time when an implanted component is replaced or "changed out", i.e., when an old implanted component (such as the pulse generator in a pacemaker system) is removed and a new component is implanted in its place. Changing out the implanted electronic component of a medical device may be required, for example, when its battery becomes depleted, or when it malfunctions.
Frequently, when the electronic component of a medical device is changed-out, it is not necessary or desirable to also remove and replace the implanted lead(s) with which it is used. Lead implantation can be a complicated procedure, and unless a lead has become worn or damaged, or has become dislodged from the proper positioning, it is usually preferable upon pulse generator change-out to merely disconnect the electronic component from the implanted lead(s), leaving the lead(s) in place for subsequent reconnection to the replacement component.
In the of a typical pacemaker, battery depletion requiring pulse generator change-out may occur five to ten years after initial implant. During this five to ten years, an implanted lead will typically become encapsulated in fibrous tissue, which is a further reason for leaving the lead in place for pulse generator change-out.
Resident inflammatory cells in the fibrous tissue surrounding an implanted pulse generator and lead become weakened or "exhausted" over time, such that at the time of pulse generator change-out, the amount of bacteria which can cause infection at the implant is reduced by several orders of magnitude. Once the implant pocket becomes infected, the infection can migrate along the lead sheath to the heart. Given the exhausted inflammatory system locally, such a migrating infection can become intractable and life-threatening. Removal of the pulse generator and lead is then necessary to cure the infection. However, as noted above, removal of a chronically implanted lead can be difficult and dangerous, and in some cases could require a thoracotomy.
In view of the foregoing, it is believed that it would be desirable to provide a means to prevent the chronic migration of infections along the length of an implanted lead.